The present invention relates to a thin film magnetic disc for a magnetic disc memory used as an external memory such as a computer, work station or personal computer and a method of manufacturing the thin film magnetic disc, and particularly to a thin film magnetic disc including a protective layer having an excellent disc durability and a method of manufacturing the thin film magnetic disc.
In recent years, there has been a need for to increase the capacity of a magnetic disc to hold information, as well as a need to reduce the size and weight of a magnetic disk memory. To make both the needs compatible with each other, it is essential to significantly improve the recording density of a magnetic disc as a recording medium. Current magnetic discs mainly are constructed of a sputtered thin film type in which a chromium under layer, a cobalt alloy magnetic layer and a carbon protective layer are formed by sputtering on a nonmagnetic substrate composed of a nickel-phosphorus plated aluminum based alloy and wherein the surface of the protective layer is coated with a lubricant. In such a sputtered thin film magnetic disc, it is necessary to make narrower a spacing between a recording film of the magnetic disc and a head for realizing a higher density. To satisfy this need, the thickness of the protective layer is required to be made thin in order to lower a flying height of the head. The thinning of the protective layer, however, presents disadvantages in lowering disc durability and reliability and also in making difficult a stable running of a head at a low flying height.
One means for solving such disadvantages has been proposed in Japanese Patent Laid-open Nos. Hei 1-258223 and Hei 2-143912, wherein a protective layer is formed of two carbon layers which are different from each other in film property.
The above noted means, however, have proven to be insufficient because the total film thickness of the protective layer formed of two carbon layers is made thick, causing a spacing loss between a head and a magnetic layer. One means for reducing a spacing loss is described in Japanese Patent Laid-open No. Hei 2-49281, which is intended to ensure the strength of a contact portion with a head and to reduce an effective film thickness. The thinning of the protective layer at a recessed portion, however, allows scratches to be easily generated due to hard dust, which tends to generate corrosion and finally to cause head crush. As a result, in the related art thin film magnetic discs, it has been difficult to reduce the thickness of a protective layer to a value of 10 nm or less, and also to obtain an excellent design of disc durability for some materials of the protective layer because of incompatibility between wear resistance and lubricant adsorption of the materials.